Electrohydraulic forming-based deformation device and method

ABSTRACT

The invention relates to a method and device for shaping an object such as a tube on an insert by means of compression generated by a shock wave, e.g. in a liquid or in another medium.

CORRESPONDING APPLICATION

The present application claims priority from the prior Swiss application No. 0255/17 filed on Mar. 2, 2017 in the name of Mr. Albert Gaide, this prior application being incorporated by reference in its entirety into the present application.

FIELD OF THE INVENTION AND PRIOR ART

Electrohydraulic forming is a method which consists of deforming an object by subjecting it to the shock wave produced by an electric discharge in the liquid in which it is immersed. This technology, which was developed in part to fracture bedrock rich in hydrocarbons, has been applied more recently to the forming of sheet metal by pressing it against a forming support. The pressure generated by the shock wave, which can reach very high values, produces a superplastic deformation with little or no shrinkage after dissipation of said shock wave.

Another advantage of this method resides in the fact that the execution of this deformation occurs in a very short time in comparison with the usual forming techniques.

In a related approach, use is now made of deformation by electromagnetic forming for crimping tubes provided that these are conductors. The method does not apply, however, to most stainless steels, due to their poor electrical conductivity. In these cases, electrohydraulic forming offers an alternative, but it is not applicable without alteration for different reasons, particularly due to the anisotropy of the shock wave and due to the fact that the part to be deformed and the die on which it must be pressed are immersed in the same bath.

The invention is intended to remove these obstacles and to allow the replacement of an electromagnetic forming method by an electrohydraulic method for crimping and deforming tubes. It applies particularly, but not exclusively, to the formation of tubes made of stainless steel on forming matrices (also called “inserts” in the present application) capable of being withdrawn, or dissolved, once the deformation is accomplished.

SUMMARY OF THE INVENTION

One goal of the invention is to improve known methods and devices.

More precisely, one goal of the invention is to propose an electrohydraulic forming method and device which are effective and simple to use.

Another goal of the present invention is to propose a method and a device for forming different objects, particularly, but not exclusively, for forming sleeves, also called jackets, of cartridge cases.

In one embodiment, the invention relates to a device intended to shape an object, such as a tube, over at least one insert by means of a compression force generated by a shock wave formed by an electric arc generator. The device comprises at least one first forming cavity containing an immersion bath comprising a liquid into which the object is immersed, said immersion bath being separated into two volumes, the first volume being that in which the shock wave is deployed and the second a volume in which the immersion liquid is absent or from which it can escape under the influence of the compression force formed in the first volume, the separation between the two volumes being provided by the object to be deformed.

In one embodiment, the second volume can be created inside the object, such as a tube, by the addition of closing means such as plugs on the immersed object.

In one embodiment, the second volume is created by introducing the object into the first cavity by means of guides, the object being able to contain a plurality of inserts and passing through the cavity.

In one embodiment, the shock wave can be generated in a liquid or in another medium.

In one embodiment, the device comprises an electric arc generator for generating a wave so that it is displace in a direction near the axis of the object, and a reflection means for focusing the wave on the axis of the object.

In one embodiment, the shock wave can be focused on the object to be deformed by one or more mirrors.

In one embodiment, the device can comprise an electric arc generator generating the shock wave perpendicularly to the axis of the tube and reflectors or mirrors for generating an anisotropy of the shock wave on the object.

In one embodiment, the device can comprise a second cavity in which the shock wave is generated, said second cavity being connected to the first cavity by waveguides leading to the object to be deformed.

In one embodiment, the waveguides preferably have the same length. In one variant, the waveguides do not all have the same length.

In one embodiment, the invention relates to a method for forming an object such as a tube over at least one insert present in the object by means of a compression force generated by a shock wave, said method making use of at least one first forming cavity containing an immersion bath comprising a liquid in which the object is immersed, said immersion bath being separated into two volumes, the shock wave being deployed in the first volume, the immersion liquid being absent or being able to escape from the second volume under the influence of the compression force formed in the first volume, the separation between the two volumes being provided by the object to be deformed.

In one embodiment of the method, it is possible to create the second volume in the object by adding plugs or closing means on the object.

In one embodiment of the method, it is possible to create the second volume by introducing the object into the first cavity by means of guides, said object comprising a plurality of inserts and passing through said cavity.

In one embodiment of the method, it is possible to generate the shock wave in a liquid or in another medium.

In one embodiment of the method, it is possible to use an electric arc generator for generating the shock wave so that it is displaced in a direction near that of the axis of the object, and a reflection means for focusing the wave on the axis of the object.

In one embodiment of the method, it is possible to focus the shock wave on the object to be deformed using one or more reflectors or mirrors.

In one embodiment of the method it is possible to use an arc generator generating the shock wave perpendicularly to the axis of the object, and reflectors or mirrors to generate isotropy of the shock wave on the object to be deformed on the insert.

In one embodiment of the method, it is possible to use a second cavity for generating the shock wave, and the shock wave can be applied to the object to be deformed by waveguides connecting the second cavity to the first.

In one embodiment of the method, the waveguides preferably have the same length or different lengths, which allows offsetting the waves applied to the object.

In one embodiment of the method, it is possible to use a reflected shock wave to launch a new electrical discharge by synchronizing the reflected shock wave and the new discharge to thus create an oscillatory system maintained by lower-energy discharges, the object to be deformed being displaced at a constant speed or according to a different law in the forming cavity.

In one embodiment, the invention relates to an object obtained by the method of the invention.

Embodiments of the invention will be better understood by means of the description that follows and the appended figures in which

FIG. 1 illustrates the principle of an embodiment of the invention;

FIG. 2 illustrates an embodiment of the invention;

FIG. 3 illustrates, in section, the embodiment illustrated in FIG. 2;

FIG. 4 illustrates an embodiment of the invention;

FIG. 5 illustrates an embodiment of the invention;

FIG. 6 illustrates an embodiment of the invention;

FIG. 7 illustrates an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes at least two constituents. A first constituent relates to the means of treating an object such as a tube to be deformed and its forming die (also called an “insert”). A second constituent is intended to ensure, as much as possible, the isotropy of the shock wave to generate a pressure which is exerted radially, hence perpendicularly to the axis of the tube to be deformed.

If the tube and its forming die or immersed in the same liquid, the shock wave produces a pressure at the exterior of the tube, but also in the interior. However, the shock wave cannot press the tube on its die because the liquid which is in the interior of the tube is exerting a contrary pressure. To mitigate this disadvantage, it is appropriate to create two separate volumes in the immersion bath. One in which the shock wave will be deployed and the other in which resistance to the shock wave will be inhibited, either by the absence of liquid or by the possibility that the latter will flow away freely under the influence of the pressure exerted on the exterior of the tube.

The separation between these two media can be provided for example by the tube which will be deformed. This can be achieved for example by plugging its ends as illustrated in FIG. 1, which shows a tube to be formed 2 containing two inserts 1, head to head, on which the plugs 3 are supported. An arrangement which can also be advantageous in mass production consists of installing in the tube 2 to be shaped a full series of inserts 1 (namely a plurality of inserts), preferably interlocked with one another, an example of a configuration of this type with a plurality of inserts in a tube being given in application PCT/IB2017/055079 filed on Aug. 23, 2017 in the name of Mr. Albert Gaide. The tube 2 in question can then pass through the compression/forming cavity (also called an “enclosure”) by passing through cylindrical guides 20, 21 that are slightly larger in diameter. This execution of a tube 2 passing through guides 20, 21 is for example illustrated in FIGS. 2 and 3. As long as the guides 20, 21 are sufficiently long, the pressure drop between the ends of these guides can be sufficient so that they will behave as if they were plugged and not perturb the shock wave. Seals and/or tightening devices, situated for example on the guides 20, 21, can improve the fluid-tightness of the system.

Reference 6 illustrates the arc generated by an electric arc generated in the cavity to create the shock wave. In the end, a formed tube 7 is obtained having the shape of the inserts 1 which is illustrated at the bottom of FIG. 1.

On the other hand, if the shock wave is generated at any point of the space containing the immersion liquid, it will surround the tube to be deformed but it is not certain that the pressure generated from the side facing it will be the same as that which is generated on the side that does not face it. Consequently, if the compression produced by the shock wave is not isotropic, it is not certain that the deformation of the tube is radially uniform, which results in products probably having flaws.

To mitigate this disadvantage, it is proposed to use the properties which govern the propagation of waves to obtain isotropy of pressure on the object to be deformed such as the tube 2. This, containing the inserts 1, is introduced into the cavity 5 by the entrance guide 20 and leaves the cavity by an exit guide 21. In the embodiments illustrated in FIGS. 2 and 3, the shock wave is generated by an electric arc generator 22 placed near the axis of the tube 2 to be deformed in such a manner that the shock wave generated by the electrical discharge of the generator is displaced in a direction near that of the axis of the tube 2 to be deformed. This wave is then focused on the axis of the tube by means of a concave reflector 10, which concentrates the pressure all around the part to be deformed 2 to compress it radially until it presses against the die 1 placed at its center. The cavity 5, which is shaped like a megaphone, is designed so as to favor the propagation of the shock wave around the tube 2.

Another approach, illustrated in FIGS. 4 and 5 and leading to a similar result, consists of generating the shock wave in an exterior cavity (spherical for example) 23 and connecting the latter to the immersion cavity 5 by waveguides 24 of the same length grouped around the object to be deformed 2 (a tube for example). They thus generate a radial pressure which will deform the tube 2 uniformly. Finally, by inclining the waveguides 24 with respect to the axis of the object to be deformed, it is possible to avoid a frontal collision of the shock waves originating in the different waveguides 24.

The length of the tubes 25 can also be different in order, for example, to generate waves offset in time.

FIG. 6 illustrates a tube 7 formed on a series of inserts 1.

Another approach also leading to a similar result can be accomplished by generating around the tube 1 several shock waves, either simultaneously or slightly offset in time.

Another approach, illustrated in the embodiment of FIG. 7, is to generate the shock wave 25 by a generator, perpendicularly to the axis of the object to be deformed 2 (a tube for example) and position reflectors 26 or mirrors 27 around it allowing an improvement in the isotropy of the compression in the cavity 5.

In these various executions, aside from that where the shock wave is generated in an external cavity 23, it is possible to use the reflected shock wave to launch a new electrical discharge. Finally, by synchronizing the reflected shock wave and the new discharge it is possible to create an oscillatory system which can be maintained by lower-energy discharges. The tube to be deformed is then displaced at a constant speed, or according to a different law.

The embodiments described are given by way of illustrative examples and should not be considered limiting. Other embodiments can use means equivalent to those described, for example. The embodiments and constituents of the present invention can also be combined together depending on the circumstances, or means used in one embodiment can be used in another embodiment.

Typically, as a non-limiting exemplary embodiment, the present invention can be used to form cartridge cases for firearms from tubes. Other implementations are of course possible within the scope of the present invention and by using the method and the principles described in the present application applied to other objects which will be deformed over one or more inserts or forms/dies according to the principles of the present invention. 

1.-20. (canceled)
 21. A device intended for shaping a tube, on at least one insert present in the tube, by means of a compression force generated by a shock wave formed by an electric arc generator, said device comprising at least one first forming cavity containing an immersion bath into which the tube is immersed, said immersion bath being separated into two volumes, the first volume being that in which the shock wave is deployed and the second a volume in which the immersion liquid is absent or from which it can escape under the influence of the compression force formed in the first volume, the separation between the two volumes being provided by the tube to be deformed.
 22. The device according to claim 21, wherein the second volume is created in the tube by the addition of plugs to the ends of the immersed tube.
 23. The device according to claim 21, wherein the second volume is created by introducing the tube into the first cavity by means of guides, said tube comprising a plurality of inserts and passing through said cavity.
 24. The device according to claim 21, wherein the shock wave is generated in a liquid or in another medium.
 25. The device according to claim 21, comprising an arc generator for generating the wave so that it is displaced in a direction near that of the axis of the tube, and a reflection means for focusing the wave on the axis of the tube.
 26. The device according to claim 21, in which the shock wave is focused on the object to be deformed by one or more mirrors.
 27. The device according to claim 21, comprising an arc generator generating the shock wave perpendicularly to the axis of the tube and reflectors or mirrors for generating isotropy of the shock wave on the tube.
 28. The device according to claim 21, said device comprising a second cavity wherein the shock wave is generated, said second cavity being connected to the first cavity by waveguides leading to the tube to be deformed.
 29. The device according to claim 28, wherein the waveguides have the same length or a different length.
 30. A method for shaping a tube over at least one insert present in the tube by means of a compression force generated by a shock wave, said method making use of at least one first forming cavity containing an immersion bath comprising a liquid into which the tube is immersed, said immersion bath being separated into two volumes, the shock wave being deployed in the first volume, the immersion liquid being absent or being able to escape from the second volume under the influence of the compression force formed in the first volume, the separation between the two volumes being provided by the tube to be deformed.
 31. The method according to claim 29, wherein the second volume is created in the tube by the addition of plugs at the ends of the tube.
 32. The method according to claim 30, wherein the second volume is created by introducing the tube into the first cavity by means of guides, said tube comprising a plurality of inserts and passing through said cavity.
 33. The method according to claim 30, wherein the shock wave is generated in a liquid or in another medium.
 34. The method according to claim 30, wherein the arc generator is used to generate the wave so that it is displaced in a direction near that of the axis of the tube, and a reflection means for focusing the wave on the axis of the tube.
 35. The method according to claim 30, wherein the shock wave is focused on the object to be deformed using one or more reflectors or mirrors.
 36. The method according to claim 30, wherein an arc generator generating the shock wave perpendicularly to the axis of the tube and reflectors or mirrors are used to generate isotropy of the shock wave on the tube.
 37. The method according to claim 30, wherein a second cavity is used to generate the shock wave, the shock wave is applied to the tube to be deformed by waveguides connecting the second cavity to the first.
 38. The method according to claim 37, wherein the waveguides have the same length or a different length.
 39. The method according to claim 30, wherein a reflected shock wave is used to launch a new electrical discharge by synchronizing the reflected shock wave and the new discharge to create an oscillatory system maintained by lower-energy discharges, the tube to be deformed being displaced at constant speed or according to a different law. 